Comparative Analysis of Three-Legged Angle Steel Towers and Three-Legged Tubular Towers

In modern communication, power transmission, and other fields, iron towers serve as crucial infrastructure. Their performance and applicability play a vital role in engineering construction. Three-legged angle steel towers and three-legged tubular towers have been widely used in various projects due to their unique structural designs and performance advantages. This article conducts an in-depth comparative analysis of these two tower types from multiple dimensions, including structural characteristics, material selection, construction techniques, performance, and cost-effectiveness. Additionally, it explores their applicability in practical scenarios, providing a comprehensive reference for engineering design and selection.

I. Comparison of Structural Characteristics

1.1 Three-Legged Angle Steel Towers

Three-legged angle steel towers utilize three angle steel columns as the main supporting structure, forming a stable triangular spatial structure through horizontal and diagonal members. This structural form draws on the geometric stability principle of triangles, enabling uniform load distribution in three directions and effectively resisting vertical and horizontal loads.

The main materials of angle steel towers are usually hot-rolled equal-angle or unequal-angle steel, with appropriate specifications and models selected according to engineering load requirements. Horizontal and diagonal members also use angle steel, which is fixed to the main materials by bolt connection or welding. In practical applications, the height of three-legged angle steel towers can be designed as required. They are generally suitable for medium and low-height engineering scenarios, such as small and medium-sized communication base stations and short-distance power line erection. Their structural characteristics allow for high load-bearing capacity within a limited footprint, making them suitable for areas with strict space requirements.

However, the lattice structure of angle steel towers has certain limitations. Due to the gaps between angle steel components, the windward area is relatively large under wind loads, resulting in significant wind load effects. Moreover, the cross-sectional characteristics of angle steel make it relatively weak in resisting torque, and local instability may occur under complex load conditions.

1.2 Three-Legged Tubular Towers

The main structure of three-legged tubular towers consists of three steel pipes as the main materials. Compared with angle steel towers, the circular or polygonal cross-section of steel pipes has better mechanical properties. The circumferential symmetry of steel pipes ensures uniform bending and torsional resistance in all directions, enabling more effective resistance to complex loads.

The connection joints of three-legged tubular towers usually adopt flange connection or intersecting welding. Flange connection facilitates on-site installation and disassembly, improving construction efficiency; intersecting welding can achieve seamless joint connections, enhancing the integrity and stability of the structure. In some projects with high requirements for structural rigidity and stability, stiffeners are also installed inside the steel pipes of three-legged tubular towers to further improve the load-bearing capacity of components.

Three-legged tubular towers have a simple and smooth appearance and a small wind resistance coefficient, which can effectively reduce the impact of wind loads. This structural form is suitable for engineering scenarios with high heights and large loads, such as large communication hubs, terminal towers, and corner towers of high-voltage transmission lines. The compactness and efficiency of their structure have gradually made them an important tower type in modern engineering construction.

II. Comparison of Material Selection

2.1 Materials of Three-Legged Angle Steel Towers

The main materials of three-legged angle steel towers are angle steel made of carbon steel or low-alloy steel. Carbon steel has good workability and weldability and is relatively low in price, making it suitable for projects with strict cost control. Low-alloy steel, on the basis of carbon steel, adds a small amount of alloying elements (such as manganese, silicon, vanadium, etc.), significantly improving the strength, toughness, and corrosion resistance of the steel, making it suitable for areas with harsh environmental conditions.

To enhance the anti-corrosion performance of angle steel, hot-dip galvanizing is usually used to treat its surface. The hot-dip galvanized layer can form a dense protective film on the surface of the angle steel, effectively isolating the steel from contact with external corrosive media and extending the service life of the tower. In a general atmospheric environment, the service life of hot-dip galvanized angle steel can reach 20 - 30 years.

2.2 Materials of Three-Legged Tubular Towers

The main materials of three-legged tubular towers usually use seamless steel pipes or high-frequency welded steel pipes. Seamless steel pipes are made through piercing and rolling processes, with high strength and uniform wall thickness, suitable for key parts bearing large loads. High-frequency welded steel pipes are formed by heating and welding with high-frequency current, featuring high production efficiency and relatively low cost. They can effectively control material costs while meeting engineering requirements.

In terms of material performance, the yield strength and tensile strength of steel pipes are generally higher than those of angle steel, providing higher load-bearing capacity for the tower. In addition, the smooth surface of steel pipes results in a small wind resistance coefficient, offering better stress performance under wind loads. To improve the corrosion resistance of steel pipes, in addition to the hot-dip galvanizing process, anti-corrosion coatings (such as epoxy zinc-rich primer, polyurethane topcoat, etc.) are also applied to form a multi-layer protection system, further enhancing the anti-corrosion ability of steel pipes and enabling them to operate stably for a long time in highly corrosive environments such as marine and chemical industries.

III. Comparison of Construction Techniques

3.1 Construction of Three-Legged Angle Steel Towers

The construction process of three-legged angle steel towers is relatively simple. First, foundation construction is carried out according to design requirements. The foundation forms usually include reinforced concrete independent foundations or pile foundations, and the specific form is determined according to geological conditions and load size. After the foundation construction is completed and reaches the design strength, the assembly of the tower begins.

The components of the angle steel tower are prefabricated in the factory and then transported to the construction site for assembly. The assembly process mainly adopts bolt connection. Construction workers splice the angle steel components piece by piece according to the drawings and fix them by tightening the bolts. This construction method has low requirements for construction equipment and technology, and can be completed by general small-scale construction teams. In some areas with complex terrain and inconvenient transportation, the light weight and easy installation of angle steel towers give them obvious advantages. However, during long-term use, problems such as bolt loosening and corrosion may occur at bolt connection joints, requiring regular inspection and maintenance.

3.2 Construction of Three-Legged Tubular Towers

The construction process of three-legged tubular towers is relatively complex. Due to the large size and heavy weight of steel pipe components, high requirements are imposed on transportation and hoisting equipment. During transportation, special transport vehicles are required, and effective fixing measures must be taken to prevent deformation of the steel pipes.

At the construction site, large cranes are usually required for the hoisting and installation of steel pipes. The connection between steel pipes adopts flange connection or intersecting welding. Intersecting welding requires a high level of technical proficiency from welders, and professional welding process evaluation and welder training are necessary to ensure welding quality. In addition, during the welding process, effective wind and rain protection measures are required to avoid welding defects.

The construction process of three-legged tubular towers requires strict quality control. Every link, from the processing and production of steel pipes, transportation, hoisting, to the construction of connection joints, needs to undergo strict inspection and acceptance. Although the construction difficulty is high, once completed, the stability and reliability of the structure can be effectively guaranteed.

IV. Comparison of Performance

4.1 Load-Bearing Capacity

In terms of load-bearing capacity, three-legged tubular towers, with steel pipes as the main materials, have a larger moment of inertia and radius of gyration of the cross-section. Under the same cross-sectional area, they can bear greater axial pressure and bending moment. Studies have shown that under the same load conditions, the load-bearing capacity of three-legged tubular towers is approximately 20% - 30% higher than that of three-legged angle steel towers. This advantage makes three-legged tubular towers widely used in projects with high load-bearing requirements, such as high-voltage transmission lines and large communication base stations.

Although the load-bearing capacity of three-legged angle steel towers is relatively lower, through reasonable structural design and component selection, they can still meet the requirements of medium and low-load projects. In the construction of some small-scale power lines and communication base stations, three-legged angle steel towers still hold important application value due to their cost advantages and good applicability.

4.2 Wind Resistance

Wind resistance is an important indicator for measuring the performance of towers. Three-legged tubular towers, with their circular or polygonal cross-sections, have a small wind resistance coefficient, which can effectively reduce the effect of wind loads. Under strong winds, the streamlined shape of steel pipes allows airflows to pass smoothly, reducing the generation of wind eddies and thus minimizing wind vibration effects.

In contrast, the lattice structure of three-legged angle steel towers has a large windward area. Under wind loads, turbulence is likely to occur in the gaps between angle steel components, leading to an increase in wind loads. At the same time, angle steel towers have poor torsional resistance and are prone to structural instability under the torsional action of wind loads. Therefore, in strong-wind areas, the wind resistance of three-legged tubular towers is significantly better than that of three-legged angle steel towers.

4.3 Seismic Performance

In terms of seismic performance, three-legged tubular towers have good structural integrity and ductility. The continuous cross-section and uniform stress characteristics of steel pipes enable them to better absorb and dissipate energy during earthquakes, reducing the degree of structural damage. In addition, the connection joints of three-legged tubular towers usually adopt rigid connection methods, further enhancing the seismic capacity of the structure.

Under earthquake action, the lattice structure of three-legged angle steel towers is prone to local damage due to the large number of connection joints between components, which may affect the overall stability of the structure. To improve the seismic performance of three-legged angle steel towers, it is usually necessary to increase support components and strengthen joint connections in the structural design to enhance the integrity and ductility of the structure.

V. Comparison of Cost-Effectiveness

5.1 Material Costs

The main material of three-legged angle steel towers is angle steel, which has a relatively low market price. At the same time, the processing technology of angle steel is simple, and the processing cost is also low. Therefore, three-legged angle steel towers have certain advantages in material costs.

The main material of three-legged tubular towers is steel pipes, which are relatively expensive, especially seamless steel pipes. In addition, the processing of steel pipes is difficult and requires professional processing equipment and technology, further increasing material costs. Statistics show that for towers of the same specification and height, the material cost of three-legged tubular towers is approximately 15% - 20% higher than that of three-legged angle steel towers.

5.2 Construction Costs

The construction process of three-legged angle steel towers is simple, with low requirements for construction equipment and technology. The labor costs of construction workers and equipment rental costs are relatively low. At the same time, the components of angle steel towers are light in weight, resulting in low transportation costs. Therefore, three-legged angle steel towers have obvious advantages in construction costs.

The construction of three-legged tubular towers requires professional equipment such as large cranes, resulting in high equipment rental costs. In addition, the welding and installation of steel pipes require professional technicians, and labor costs are also relatively high. Moreover, due to the large size and heavy weight of steel pipe components, transportation costs are high. Overall, the construction cost of three-legged tubular towers is approximately 30% - 40% higher than that of three-legged angle steel towers.

5.3 Maintenance Costs

In terms of maintenance costs, the lattice structure of three-legged angle steel towers makes component inspection and maintenance relatively easy. However, due to the large number of connection joints in angle steel towers, problems such as bolt loosening and corrosion are common, requiring regular inspection and maintenance with a relatively high maintenance frequency.

Three-legged tubular towers have good structural integrity and fewer connection joints, resulting in relatively less maintenance work. Although the maintenance cost of the anti-corrosion coating of steel pipes is high, due to its long maintenance cycle, the overall maintenance cost of three-legged tubular towers is similar to that of three-legged angle steel towers.

From the perspective of the full life cycle cost, three-legged angle steel towers have lower initial construction costs. However, due to their relatively weak load-bearing capacity and performance, reinforcement or renovation may be required in the later stage, increasing usage costs. Although three-legged tubular towers have high initial construction costs, their excellent performance ensures long-term stable operation, reducing later maintenance and renovation costs, and demonstrating better cost-effectiveness in some large-scale long-term projects.

VI. Analysis of Practical Application Scenarios

6.1 Applications of Three-Legged Angle Steel Towers

Three-legged angle steel towers, due to their low cost and convenient installation, are mainly applied in the following scenarios:

• Small Communication Base Stations: In rural areas, mountainous areas, and other regions with relatively low communication requirements, three-legged angle steel towers can meet the erection needs of small communication base stations, providing basic communication services for local areas.

• Short-Distance Power Lines: In short-distance power transmission projects such as urban distribution networks and rural power lines, three-legged angle steel towers can be used as supporting structures, showing good applicability.

• Temporary Engineering Facilities: In some temporary construction sites, event venues, etc., three-legged angle steel towers can be used as temporary lighting towers, signal towers, etc., to meet temporary usage requirements.

6.2 Applications of Three-Legged Tubular Towers

Three-legged tubular towers, with their high load-bearing capacity and good wind and seismic resistance, are mainly applied in the following scenarios:

• Large Communication Hubs: In areas with high requirements for communication capacity and signal quality, such as city centers and transportation hubs, three-legged tubular towers can support large communication equipment, ensuring the stable operation of communication networks.

• High-Voltage Transmission Lines: In high-voltage and extra-high-voltage transmission lines, three-legged tubular towers, as terminal towers, corner towers, and crossing towers, can bear huge loads, ensuring the safe and reliable transmission of electricity.

• Projects in Harsh Environments: In harsh environments such as coastal areas, strong-wind regions, and earthquake-prone zones, the excellent performance of three-legged tubular towers makes them the preferred tower type, effectively resisting the impact of natural disasters.

VII. Conclusion

Three-legged angle steel towers and three-legged tubular towers each have their own characteristics and advantages, playing important roles in different engineering scenarios. Three-legged angle steel towers are characterized by low cost and convenient installation, suitable for medium and low-load projects and those sensitive to cost. Three-legged tubular towers, with their high load-bearing capacity and good wind and seismic resistance, perform outstandingly in large-scale projects and harsh environments.

In actual engineering design and selection, multiple factors such as engineering load requirements, topographic and geomorphic conditions, environmental factors, and cost budgets need to be comprehensively considered to reasonably select the tower type, ensuring the safety, reliability, and economy of the project. With the continuous development of material technology and construction techniques, three-legged angle steel towers and three-legged tubular towers will be continuously optimized and improved, providing more high-quality solutions for modern engineering construction.